No abstract

Abstract:Although reviews of the scientific literature have failed to demonstrate conclusive evidence for the impact of rural land management on peak runoff rates, increasing emphasis is being placed by policy makers on its role in catchment-scale flood risk management. Poor soil and field conditions can lead to higher rates of runoff from extreme rainfall events; however, the improvement of land condition will lead to differing runoff responses depending on land use, soil type and climatic regime. This study has evaluated the relative impact of improvement of field and soil conditions on peak daily runoff rates for a range of soils and vegetation cover types across England and Wales. It has shown that rural land management changes could be expected to make a positive contribution to sustainable flood risk management, especially for more frequent events. The greatest relative reduction in runoff can be achieved through the improvement of degraded permeable soils under managed grassland in drier regions. Taking a plausible scenario of land management improvement in arable and grassland systems, the relative reduction in peak runoff was estimated for 518 policy units as defined in the Environment Agency's Catchment Flood Management Plans. For the 1 in 100 year event, there were only a few policy units where the expected reduction in runoff exceeded 5%. Rural land management practices which are likely to be beneficial to flood risk management may afford some protection to areas where structural measures may not be implemented for cost-benefit reasons, and may help to offset some of the anticipated increases in flood risk associated with climate change.

Flood risk is influenced by the rate and speed of rural land runoff within the catchment and by flow attenuation in the floodplain. Most research to date has demonstrated that the overall flood risk benefits of multiple small scale land management changes at a large catchment scale are difficult to determine and, in some situations, may not provide significant benefits in flood events. Measures may, however, offer potential for attenuation, improving flood warning times and therefore reducing flood damages. Climate change and major legislative drivers such as the Water Framework Directive will also further drive the need to consider different approaches to how land is managed and the impact that this may have on flood and coastal risk management.